1. Field of the Invention
The present invention generally relates to a method of forming a low-dielectric constant (low-k) material layer. More particularly, the present invention relates to a method of reducing the number of particles on a low-k material layer, and to a method of reducing simultaneously the number of particles on a low-k material layer and the fluorine concentration in the same, wherein the low-k material layer is formed in a PECVD chamber that is previously cleaned with a fluorine-containing etching gas. The present invention also relates to an integrated circuit (IC) device that includes a PECVD silicon-based low-k material layer having a fluorine concentration in the order of 105/cm3 or lower.
2. Description of Related Art
As the size of ultra-large scale integration (ULSI) devices continue to shrink, the RC-delay effect caused by the multi-level metal interconnect not only limits the high speed operation but also increases the power consumption to raise the temperature of the chips. Dielectric layers made from low-k material can be disposed between the metal interconnect layers to shorten the RC-delay time.
Nowadays, many low-k materials are formed through plasma-enhanced chemical vapor disposition (PECVE), including a material called HARD-CORAL, which uses tetramethyl-cyclotetrasiloxane (TMCTS) as reaction gas. After the low-k material layer reaches the pre-determined thickness and the source for the TMCTS gas is turned off, however, the remaining TMCTS gas would continue a deposition process, forming particles thereon. As a result, extra time and efforts are required to solve the particle issue before the mass production, thus the completion date of products will be affected.
In solution, a method to improve the particle issue of the low-k material layer. In the method, a reduced low frequency power (LF power) and a reduced high frequency power (HF power) are supplied during a delay time after the source of the reaction gas is turned off. Accordingly, the number of the particles will decrease.
FIG. 1 is the top view of a low-k material layer formed by the abovementioned deposition method. As shown in FIG. 1, though the number of the particles is reduced, the average particle number per unit area is still as many as 9697, which still affects the subsequent manufacturing process.
On the other hand, the oxide material previously deposited on the inner wall of the PECVD chamber is also a particle source, so that a fluorine-containing etching gas is usually introduced to generate plasma and remove the oxides on the chamber wall before the low-k material layer is deposited. However, after the deposition of the low-k material layer is finished, the fluorine residue of the etching gas remaining in the pipelines connecting with the chamber easily diffuse into the low-k material layer. Consequently, the interface property of the low-k material layer is degraded making the layer peel off easily, and copper atoms easily diffuse into the low-k material layer after a copper damascene structure is formed therein.